Electron velocity modulation tubes



A. VH. w. BECK ETAL 2,857,549 ELECTRON vmnocny MODULATION TUBES 5Sheets-Sheet 1 Filed July 23, 1953 A.H.W. BECK- A. B. CUTTJNG AttorneyOct. 21, 1958 A. H. w. BECK ETAL Y 2,857,549

I ELECTRON VELOCITY MODULATION TUBES Filed July 25, 1953 3 Sheets-Sheet2 w Q \r Q 0, 0) 4 w w Q1 m m I nventor A.H.W. BECK A.B.CUTT|NG A liorne y Oct. 21, 1958 A. H. w. BECK ET AL ELECTRON VELOCITY MODULATION TUBES3 Sheets-Sheet 3 Filed July 25, 1953 Inventor A.'H.W. B EC K- A.B.CUTTING A Home y United States Patent O ice 2,857,549 ELECTRON VELOCITYMODULATION TUBES Arnold Hugh William Beck and Alan Butler Cutting,London, England, assignors to International Standard ElectricCorporation, New York, N. Y.

Application July 23, 1953, Serial No. 369,805

Claims priority, application Great Britain August 1, 1952 8 Claims. (Cl.3155.47)

The present invention relates to electron velocity modulation tubes, andin particular to a novel construction of klystron amplifier tube.

In a two-resonator klystron amplifier tube an electron beam is projectedacross an input resonator so as to be velocity modulated by theelectromagnetic field therein; the beam continues through a drift spacein which the electrons become bunched and is then projected across anoutput resonator in which the bunched beam delivers up kinetic energy ofthe electrons in generating in the output resonator an electromagneticfield of greater energy than that supplied to the input resonator. Forefiicient amplification it is desirable that the equivalent shuntresistance of the output resonator be as high as possible. As with alltuned circuits, for a given bandwidth the shunt resistance is inverselyproportional to the capacitance of the circuit, which, therefore, shouldbe as low as possible. For efiicient conversion of kinetic energy intoelectric energy of the field, it is necessary that the average transittime of an electron within the field be carefully chosen. In general ashort transit time is desirable. This is achieved by allowing theelectron beam to interact with the field at one or more short gaps whoseboundaries of necessity contribute capacitance to the resonator. In manyklystrons the resonators are of re-entrant form, the inter-action gapsbeing formed between the re-entrant portions. In the present inventionthe resonators are of generally cylindrical form and a sectionaliseddrift tube, positioned on the axis of the resonator is provided withgaps in which the beam may inter-act with the resonator field. Thecapacitances of these gaps are thus in series with one another and hencethe total capacitance due to the electron system may be kept quitesmall, so that a high equivalent shunt resistance is obtained.

According to the present invention, there is provided a two-resonatorklystron amplifier tube comprising: cylindrical input and outputresonators positioned end to end along a common axis, a multi-sectioneddrift tube extending the length of the said common axis, one of thedrift tube sections communicating between the input and outputresonators and the remainder of the sections intermediate the ends ofthe respective resonators being separated from one another by gaps;means for projecting a beam of electrons through the said drift tube,the said gaps between successive drift tube sections being of suchlength that the transit angles of an unmodulated electron of the saidbeam in each said gap is 211- radians; and respective coupling means forinjecting electromagnetic wave energy into the input resonator and forextracting electromagnetic wave energy from the output resonator.

An embodiment of the invention will be described with reference to theaccompanying drawings in which:

Fig. 1 shows, in part section, one view of a tube according to thepresent invention, the section being taken in the plane II of Fig. 2;

Patented Oct. 21, 19 58 Fig. 2 is a further sectional view taken throughthe plane ]1]I of Fig. 1; and

Fig. 3 is a view, in part section, looking towards the tube from theleft of Fig. 1. V

The two resonators of the embodiment shown in the drawings are formed asa single copper block whose wall is indicated at 1. The block issub-divided into two by a central transverse wall 2, which may be formedintegrally with the cylindrical wall 1. End plates 3 and 4, closing theends of the cylinder, are bonded to the wall 1, by for example, a golddiffusion process. A sectionalised dn'ft tube 5 extends along the commonaxis of the two resonators, one of the sections 6 being secured in acentral aperture of the dividing wall 2. The remaining drift tubesections are separated by inter-action gaps of such length that thetransit angle of an unmodulated beam electron in each gap is 21rradians. These intermediate drift tube sections are supported at theirmedial planes by respective radial rods 7 and 8 (Fig. 3) secured in thewall 1. The rods securing adjacent drift tube sections are located onopposite sides of the axis of the resonators, so as to reduce as much aspossible the capacitance between drift tube sections. In the embodimentillustrated four intermediate drift tube sections are used in eachresonator, so providing five inter-action gaps in each resonator. Therods may conveniently be made of copper plated tungsten so as to combinestrength and rigidity. When the resonators oscillate in a pure T. M.mode the electric lines of force are everywhere parallel to theresonator axis, so that the drift tube support rods do not disturb thefield configuration.

A pair of cups of magnetic material, 9 and 10, are secured in centralapertures of the respective end plates 3 and 4. Cup 9 houses an electrongun, cup 10 an electron collector electrode. These cups form pole piecesfor a focusing magnet, not shown, which completes a focusing system ofthe kind described and claimed in an application of A. H. W. Beck,Serial No. 176,925, filed August 1, 1950. Each cup has secured to it asheet metal member 11 suitable for scaling to glass. The cup 9 housingthe electron gun is closed by a glass member 12 sealed to member 11,member 12 is carrying lead-out pins 13 for connection to an indirectlyheated cathode 13 which is located in cup 9 by means of an insulatingwasher 15. The collector cup is closed by a glass collar 16 and an endplate 17 sealed to the glass, the end plate carrying a copper collectorelectrode 18. Both cups 9 and 10 are shown provided with portions 19which form continuations of the drift tube 5.

Input and output connections to the respective resonators are providedby means of sections of rectangular wave guide 20 and 21 which are letinto the cylindrical resonator wall 1 and are secured by means of anouter metal cylinder 23 surrounding the resonator block between the endplates 3 and 4. The wave guide sections 20 and 21 are terminatedexternally in a flange 24 by means of which the klystron amplifier maybe coupled to further wave guide circuits. Secured to the flange 24 aretwo tuned diaphragms 25 and 26 provided with glass windows 27 separatingthe evacuated portion of the apparatus from the outside atmosphere.

Tuning of the resonators is accomplished by means of tuning strips 28whose sides are mounted in trunnions 29 free to rotate in the wall 1 ofthe resonator block parallel to the cylindrical axis thereof. The endsof the strips 28 are provided with spring fingers 30 which contact theend surfaces of the respective resonators. The strips 28 are attached torespective piston rods 31 and 32 projecting through the resonator wall 1and surrounding cylinder 23. This type of tuning mechanism forms thesubject matter of U. S. Patent No. 2,737,631 granted March 6, 1956, onan application filed May 3, 1951. The piston rods 31 and 32 are securedto the respective base members 33 and 34 of a pair of metal bellows 35and 36. The 'otherends'of the bellows 35 and 36 are secured to the outerends of members23 asshown at 37, 38, 39, and 40. Ducts 41 in the wall 1and cylinder 23 are provided for evacuating the interior of the bellows.The bellows and external tuning controls are supported between the topand bottom plates 3 and 4 of theresonators by means of the members 42and 43. The base member 34 of bellows 36 is secured to a cross piece 44,freeto slide in. guides 45 and 46 in the respective members 421and43, bymeans of a rod 47 directly bolted to the cross member and fixed to thebase member 34. The base member 33 of bellows 35 is provided with arearwardly extending screwed rod 48 free to move axially in the crossmember '44, the position of the base member 33 being 'adjustableby meansof the knurled nut 49 which is located between channel walls of thecross member 44. The cross member 44 carries a screwed rod 50 free toslide in a bushing 51 which is secured to an end plate 52 which, inturn, joins the ends of members 42 and 43. The rod 50 is provided with aknurled nut 53 by means of which the cross member 44 may be moved alongthe guides 45 and 46 so providing axial movement of the base members 33and 34 and hence simultaneous adjustment of the tuning strips 28.Adjustment of the nut 49 provides for differential tuning of theresonators.

While the principles of the invention have been described above inconnection with specific embodiments, and particular modificationsthereof, it is to be clearly understoodthat this description is madeonly by way of example and not as a limitation on the scope of theinvention.

What we claim is:

1. A two-resonator klystron amplifier tube for operation over a givenfrequency band, comprising: cylindrical input and output resonatorspositioned end abutting end along a common axis; a multi-sectioned drifttube extending the length of the said common axis, one of the drift tubesections communicating between the input and output resonators and theremainder of the sections intermediate the ends of the respectiveresonators being separated from one another by gaps; means forprojecting abeam of electrons through said drift tube, and respectivecoupling means for injecting electromagnetic wave energy into the inputresonator and for extracting electromagnetic wave energy from the outputresonator, the said gaps between successive drift tube sections being ofsuch length that the transit angle of an unmodulated electron of thesaid beam in each said gap is 2w radians-at the midband of the operatingfrequency of said tube.

2. An amplifier tube according to claim 1, in which the drift tubesections intermediate the ends of the respective resonators, are eachsupported by a radial rod secured to the wall of the said resonator,alternate rods lying on opposite sides of the axis.

3. A n amplifier tube according to claim 1 said drift tube section, anda pair of end plates mechanically bonded to the resonator block; and inwhich cups of ferromagnetic material, 'forminglpole pieces for magneticfocusing of the electron beam, housing respectively an electron gun anda collector electrode, are secured in central apertures in therespective end plates. 7 y

4. An amplifier. tube according to claim 3 in which the said cuphousingthe electron gun comprises a sleeve of an alloy sealing readilyto glass secured to the said ferromagnetic material and to a glass cap,an indirectly heated cathode being mounted in thesaid cup, and leads tosaid cathodes being sealed through the said glass cap.

5. An amplifier tube according to claim 3 in which the said collectorcup comprises a cylinder of ferromagnetic material closed at the endadjacent the resonator to which it is secured by a centrally aperturedwall, an alloy sleeve sealing readily to glass secured to the saidferromagnetic member and to a glass collar, and a metal closure memberforming a cap secured to the said glass collar and supporting anelectron collector electrode centrally in the said cup. 7

6. An amplifier tube according to claim 3, in which each said resonatorcommunicates through a port, respectively, to sections of rectangularwave guide secured in the said ports, each said wave guide section beinghermetically sealed by means of a window of vitreous or ceramic materialsealed to a tuned diaphragm mounted in the said wave guide section.

7. An amplifier tube according to claim 3 in which each said resonatorcomprises a tuning member extending from end to end of the resonator andshort circuiting the end walls thereof, means being provided foradjusting the positions of the tuning members by respective piston rodspassing through the resonator wall.

' 8. An amplifier tube according to claim 7 in which the said adjustingmeans comprises a pair of 'metal bellows, one secured adjustably and theother fixed to a cross member free to slide in guides in a pair ofsupporting members securedto the resonator block, and means foradjusting the base of one bellows with respect to the cross member andindependent means for adjusting'the position of the said cross memberwith respect to the support members.

References Cited in the file of this patent 2 UNITED STATES PATENTSNorton et a1 Nov. 25, 1952 jpII'M

